Keyboard printed circuit switch assembly with axially movable coil spring contact and associated key type actuator

ABSTRACT

A key operated switch incorporated with a printed circuit board having conductors thereon and an upwardly extending conical post of non-conducting material between adjacent terminals of certain of the conductors. An expandable toroidal contact spring surrounds the post and is normally located above the conductors by virtue of its constriction against the conical surface. A depressible key member, which is normally held in raised position by the contact spring, is effective upon depression to move the spring into bridging contact with the conductors.

United States Patent [191 Berry 5] May 22, 1973 KEYBOARD PRINTED CIRCUIT 959,435 5/1910 Thomson ..200/ 166 BA SWITCH ASSEMBLY WITH AXIALLY 1,333,115 3/1920 Jones ..200/166 BA MOVABLE COIL SPRING CONTACT g g 85 AND ASSOCIATED KEY TYPE or ec ACTUATOR Primary Examiner-J. R. Scott 75 Inventor: William A. Berry, Covina, Calif. Attorney-Fred Sehwend [73] Assignee: Addmaster Corporation, San [57] ABSTRACT Gabriel, Calif. A key operated switch incorporated with a primed cir- [22] filed: Sept 1971 cuit board having conductors thereon and an up- 21 APPL 1 0 wardly extending conical post of non-conducting material between adjacent terminals of certain of the conductors. An expandable toroidal contact spring [52] US. Cl. ..200/l6 A, 200/5 R, ZOO/61.76, Surrounds the post and is normally located above the ZOO/159 R, 200/ 166 BA conductors by virtue of its constriction against the Int- Cl. conical surface A depressible key member is of Search R, A, B, normally in raised position the ontact pring, 200/61-76, 159 R, 166 BA is effective upon depression to move the spring into bridging Contact with the conductors. [56] References Cited 8 Claims, 3 Drawing Figures UNITED STATES PATENTS 10/1972 Huggard ..200/61 19 KEYBOARD PRINTED CIRCUIT SWITCH ASSEMBLY WITH AXIALLY MOVABLE COIL SPRING CONTACT AND ASSOCIATED KEY TYPE ACTUATOR BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to electric switches, and has particular reference to depressible key operated switches for use with printed circuit boards wherein the circuits are formed by printing or etching conductors on an insulated base or board.

2. Description of the Prior Art Switches have been developed heretofore for use in connection with printed circuit boards to control electronic circuits. Generally, control of such an electronic circuit requires a signal of adequate voltage, although the current requirements are generally small. Accordingly, it is necessary that the switch contacts be clean and free from metal oxides, etc., which might otherwise increase the resistance of the contacts to a point where the signal will be unreliable. Also, it is essential in many cases that the switch contacts do not produce noise or contact bounce or chatter which may give rise to spurious and unwanted signals.

Heretofore, switches of the above type have generally been constructed to provide a certain amount of wiping action between the switch contacts to remove any oxides or dirt that may accumulate. The U.S. Pat. to Fordeck No. 3,206,561 issued on Sept. 14, 1965, is an example of such a switch. The latter discloses a toroidal helically wound spring which, when the key is depressed, slides over the conductors of a printed circuit board to make contact. Although such a switch is generally satisfactory, it has been discovered that the sliding movement of the many coils of the spring over the printed circuit conductors gives rise to a certain amount of noise which in many cases is undesirable.

Other switches, as disclosed for example, by the U.S. Pat. to Andren No. 3,523,163, issued on Aug. 4, I970, produce a snap action of the switch contacts which tend to insure good electrical contact. However, such switches tend to cause the contacts to bounce" which may give rise to unwanted multiple signals.

Although it is well known that certain of the noble metals, such as gold and platinum, are relatively free from oxidation and therefore make excellent switch contacts, such metals are very expensive and therefore cannot be used in relatively inexpensive switches unless they are applied to a base metal as an extremely thin plating or coating. However, it has been found that continued wiping action of the contacts of prior art switches tends to wear off such thin coating, thereby exposing the base metal to oxidation.

SUMMARY OF THE INVENTION According to the present invention, a relatively simple and inexpensive switch employing a toroidal, helically wound spring contact is provided in which no wiping action occurs between the contact spring and the conductors, thereby allowing a very thin coating of non-oxidizing metal, such as gold, to be applied to the contact points. Although this coating may be extremely thin, i.e., on the order of 0.000050 inches in thickness, it will insure adequate electrical contact and since there is no wiping or abrading action between the contact points there will be no tendency for the coating to wear.

Further, since there is negligible or no wiping action between the contacting points, no noise is generated. Also, since no snap or violent contact action is involved, contact bounce or chattering is eliminated.

Further, since a toroidal, helically wound contact spring is employed to effect the electrical contact, the many coils of the spring provide multiple points of contact effective to insure adequate electrical connection regardless of any minor imperfections in any one coil.

An additional feature of the invention is that the switch is simple and inexpensive to manufacture and assemble and yet is compact so that multiple number of said switches can be grouped together to form a keyboard switching system.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a sectional view through a switch assembly embodying a preferred fonn of the present invention.

FIG. 2 is a sectional plan view taken along line 2-2 of FIG. 1.

FIG. 3 is a sectional plan view taken along 3-3 of FIG. 1.

DESCRIPTION OF THE ILLUSTRATED EMBODIMENT Referring to the drawing, a single key operated switch, generally indicated 11, is illustrated. However, it is to be understood that a large number of such switches can be grouped together to form a keyboard switching assembly.

A printed circuit board 12 plastic or similar nonconductive material is provided having two or more conductors 13 and 14 formed on the upper surface thereof.

A hole 15 is drilled or otherwise formed through the board intermediate the terminal ends of the conductors to receive a hollow post 16 of plastic or other nonconductive material. The post has a pair of diametrically opposed yeilable prongs 17 formed integrally therewith and terminating in barbs 18. When the prongs are fully inserted in the hole 15, such barbs spring outwardly to securely lock the post in a centered position over the hole.

The post has a vertical hole 19 extending concentrically therethrough and an upwardly converging conical surface which terminates in a flange 20 at its upper end.

A toroidal helically wound metal contact spring 21 is streched over the post and because of its constriction against the conical surface it normally maintains itself in its upward full line illustrated position in FIG. 1, where it may engage the flange 20. Thus, the flange 20 prevents the spring 21 from becoming removed from the top of the post especially during assembly of the switch parts.

A depressible key is provided including a keytop 22 and a keystem 23 suitably attached thereto. The keystem is rectangular in cross section at its upper end and is slidably mounted in a mating slot 24 formed in a key guide plate 25 which extends in spaced parallel relation to the circuit board 12.

The keystem has an annular skirt 124 integral therewith, whose bottom edge 26 rests on and is supported by the contact spring 21. The lower end of the keystem 23 terminates in a cylindrical guide plunger 27 which is guided for vertical movement within an inwardly extending bearing flange 28 formed midway along the length of the hole 19 in the post 16. Thus, the post 16 and key frame 25 will vertically guide the key during the depression thereof. Since the slot 24 and bearing flange 28 are relatively short in length they will tolerate an appreciable mis-alignment of each other without binding the keystem against sliding movement.

It will be noted that the upper end of the skirt limits against the key frame 25.

Preferably, a flash coating of gold, platinum or similar noble metal having little or no tendency to oxidize and having a thickness of approximately 0.000050 inches is applied to both the spring 21 and the conductors l3 and 14.

It will be noted that upon depression of the keytop 22, the skirt 124 will cause the spring 21 to roll down the conical surface of the post until it contacts the conductors 13 and 14, thereby establishing an electrical circuit across these conductors.

It will also be noted that the conical surface is divided into two sections, one shown at 30 having a relatively great angular diversion and the remaining section 31 having a lesser angular diversion. Thus, at the commencement of a key stroke, a greater resistance to depression will be met and thereafter the key stroke will be materially easier as the contact spring 21 moves over the section 31. Such contour and the resulting key action may, however, be varied as desired.

It will be noted that by enlarging the adjacent terminal ends of the conductors 13 and 14 to substantially surround the hole 15, as indicated at 32 and 33 in FIG. 3, a majority of the coils of the contact spring 21 will be utilized to establish electrical contact.

Alternatively, the plunger 27 may be omitted whereby the keystem may be guided solely by the bearing 24 in the keyframe 25 or the bearing 28 may be greatly enlarged whereby the keystem may be guided solely by the bearing 28.

An important feature of the invention is the ease of assembly of the key operated switch or group of such switches. In this case, the post 16 is merely snapped to the hole 15, the spring 21 is placed over the post and the key guide plate 25 with the keytop 22 and keystem 23 assembled thereon, is merely located in position with the plunger 27 fitted into the hole 19 of the post.

I claim:

1. A key operated switch comprising a printed circuit board of non-conductive material having a plurality of conductors on the upper surface thereof, and spaced from each other,

a post of non-conductive material supported by said board adjacent said conductors,

said post having an upwardly converging surface,

a toroidal spring contact member of conductive material tensioned over said upwardly converging surface,

said spring contact member being normally elevated on said post by virtue of its constriction against said upwardly converging surface,

and a depressible key member for moving said spring contact member downwardly over said post and into contact with said conductors.

2. A key operated switch according to claim 1 comprising means on said post for vertically guiding said key.

3. A key operated switch according to claim 1 comprising a key plate having a bearing therein for vertically guiding the upper end of said key member,

and said post having a second bearing therein for vertically guiding the lower end of said key member.

4. A key operated switch according to claim 1 comprising means at the upper end of said post for limiting upward movement of said spring contact member.

5. A key operated switch according to claim 1 wherein said board has an opening therein extending between a pair of said conductors,

and said post has a plurality of downwardly extending yieldable prongs fitted in said opening whereby to locate said post between said conductors.

6. A key operated switch according to claim 1 wherein said converging surface comprises sections of different angular convergence.

7. A key operated switch comprising a printed circuit board of non-conductive material having a pair of conductors on the upper surface thereof and spaced from each other,

said board having an opening therethrough intermediate said conductors,

a post of non-conductive material having a plurality of yieldable prongs engaging the sides of said opening whereby to locate said post intermediate said conductors,

said post having an upwardly converging surface,

a toroidal spring contact member of conductive material tensioned over said converging surface,

a depressible key member,

a key guide element having a bearing for guiding the upper end of said key member for vertical movement,

said post having a bearing therein for guiding the lower end of said key member for vertical movement,

and an annular element on said key member intermediate said bearings,

said annular member engaging said spring contact member and effective to move said spring contact member over said post and into contact with said conductors upon depression of said key member.

8. A key operated switch according to claim 7 wherein said spring contact member is normally effective to raise said key member to an undepressed condition. 

1. A key operated switch comprising a printed circuit board of non-conductive material having a plurality of conductors on the upper surface thereof, and spaced from each other, a post of non-conductive material supported by said board adjacent said conductors, said post having an upwardly converging surface, a toroidal spring contact member of conductive material tensioned over said upwardly converging surface, said spring contact member being normally elevated on said post by virtue of its constriction against said upwardly converging surface, and a depressible key member for moving said spring contact member downwardly over said post and into contact with said conductors.
 2. A key operated switch according to claim 1 comprising means on said post for vertically guiding said key.
 3. A key operated switch according to claim 1 comprising a key plate having a bearing therein for vertically guiding the upper end of said key member, and said post having a second bearing therein for vertically guiding the lower end of said key member.
 4. A key operated switch according to claim 1 comprising means at the upper end of said post for limiting upward movement of said spring contact member.
 5. A key operated switch according to claim 1 wherein said board has an opening therein extending between a pair of said conductors, and said post has a plurality of downwardly extending yieldable prongs fitted in said opening whereby to locate said post between said conductors.
 6. A key operated switch according to claim 1 wherein said converging surface comprises sections of different angular convergence.
 7. A key operated switch comprising a printed circuit board of non-conductive material having a pair of conductors on the upper surface thereof and spaced from each other, said board having an opening therethrough intermediate said conductors, a post of non-conductive material having a plurality of yieldable prongs engaging the sides of said opening whereby to locate said post intermediate said conductors, said post having an upwardly converging surface, a toroidal spring contact member of conductive material tensioned over said converging surface, a depressible key member, a key guide element having a bearing for guiding the upper end of said key member for vertical movement, said post having a bearing therein for guiding the lower end of said key member for vertical movement, and an annular element on said key member intermediate said bearings, said annular member engaging said spring contact member and effective to move said spring contact member over said post and into contact with said conductors upon depression of said key member.
 8. A key operated switch according to claim 7 wherein said spring contact member is normally effective to raise said key member to an undepressed condition. 